The present invention relates generally to storage systems and, more particularly, to methods and apparatuses that utilize large capacity disk drives.
The capacity of a single HDD (Hard Disk Drive) unit provided by HDD vendors is increasing at a rapid rate in the HDD market. The capacity of a SSD (Solid State Disk) unit is also increasing. In order to avoid loss of data due to the failure of a disk unit, most storage systems adopt data protection with redundancy such as mirroring and RAID technology. As disclosed in “A Case for Redundant Arrays of Inexpensive Disks (RAID)” by D. A. Patterson, G. Gibson and R. H. Kats, published in Proc. ACM SIGMOD, pp. 109-116, June 1988, RAID configurations are classified in accordance with so-called RAID levels. RAID4, RAID5 and RAID6 configurations use parity code generated from stored data as redundant information. By using the parity code, data stored in multiple disks in a distributed manner can be reconstructed for an occurrence of a disk failure. In this manner, high data availability is accomplished. In the article, having the same data in multiple disks, so called mirroring, is introduced as one method to protect data and is categorized as RAID1.
U.S. Pat. No. 7,386,758 discloses an Object-based Storage Device (OSD) that uses RAID technology and perform reconstruction of data according to the OSD's information indicating where each object is stored in the OSD.
Because the recovery of data is achieved by copying and/or generating the same data as the data stored in the failed disk, the recovery process needs considerable time. This disk failure causes the following influences from occasion of the disk failure to completion of the recovery: the reduction of possibility to avoid unavailability and data loss due to the reduction of redundancy, and the deterioration of performance due to the load of copying data.
Applying large capacity disk drives causes the lengthening of the above duration because the amount of data to be recovered becomes large in comparison with using traditional small capacity disk drives. Therefore, a disk failure recovery method that aligns to the users' applications and usage is required at present.